Bristle Bots are cheap, easy to build and basically pure fun.
These are the parts you need to build one.
a toothbrush with angled bristles
double sided sticky tape
a 3V coin cell battery
a vibra motor
The first thing that you would have to do is to clip off the brush head from the toothbrush.
Next put some sticky tape on the top of the brush head.
The tape holds the motor in place later on. Alternatively you could glue the motor to the brush head. Now prepare the motor. You have to solder on some short wires which you can bend so that you have some kind of battery holder.
Place the LED within the bristles with the connection wires facing to the cut off end of the brush head.
Bend the connection wires around to the top of the brush head. Place the motor on the sticky tape with the soldered on wires facing to the cut off end of the brush head.
For better stability you can also tape the motor on the sides of the brush but it shouldn't be necessary.
Solder the connection wires of the motor and the LED together. The motor has no polarity to worry about, but the LED does. So make sure to remember which connection wire of the LED is the positive one (the longer wire) as this defines in which way you place the battery.
Congratulations, that was all it took.
Place your battery with its positive side touching the positive wire of the LED and enjoy the show.
Notice that I only used two batteries in this video because they were both nearly empty. Normally a fresh single one does the job. The motor still works but the LED might turn off if it gets empty over time.